Argon is an inert gas which is used in diverse applications such as welding, electric appliances, inert atmospheres in steel production, etc. Lately, its demand has increased substantially due to the rapid growth of the semiconductor industry. In the semiconductor industry, Ar of an extremely high purity is normally used. As a result, there is a need for processes to produce Ar with substantially low concentrations of O.sub.2.
Traditionally, Ar is produced from air in a cryogenic air separation plant, wherein, in addition to the recovery of O.sub.2 -- and N.sub.2 -rich streams, a crude Ar stream containing about 94-97% Ar, about 3-5% O.sub.2, and about 0.01-1% N.sub.2 is also recovered. The crude Ar stream is then further purified to produce a high purity Ar stream. In the first step of a typical purification scheme, crude Ar is mixed with H.sub.2 and passed through a catalytic hydrogenation unit, such as a Deoxo process, to react O.sub.2 with H.sub.2 to form water. The water is then removed, and the remaining gas stream is sent to a cryogenic distillation unit to remove the N.sub.2. Depending on the concentration of O.sub.2 in the crude Ar stream and the required O.sub.2 content in the final product, the amount of H.sub.2 consumed by this process can be fairly high. The cost of H.sub.2 contributes a significant fraction to the overall cost of the purification process. Moreover, in some instances due to the particular location of the air separation plant, an inexpensive H.sub.2 source may not be available. As a result, there is a need for purification processes which either do not use H.sub.2 or substantially decrease the amount that is required.
Attempts have been made in the past to purify crude Ar without the use of H.sub.2. All these processes remove O.sub.2 by its preferential kinetic adsorption on carbon molecular sieves. Details of such processes can be found in U.S. Pat. No. 4,477,265 assigned to Air Products and Chemicals, Inc.
U.S. Pat. No. 4,144,038, discloses a process wherein crude Ar from a cryogenic air separation plant is first passed through a bed of molecular sieve carbon for selective adsorption of O.sub.2 ; and the unadsorbed effluent, lean in O.sub.2, is passed through a zeolite bed for selective adsorption of N.sub.2. In this patent, both adsorbents are packed in the same column, and regeneration of the column is performed by simultaneous vacuum desorption of both adsorbents in the column.
U.S. Pat. No. 4,477,265 teaches a sequence of N.sub.2 and O.sub.2 removal by adsorption which is the opposite to that taught in the above-mentioned U.S. Pat. No. 4,144,038. In this patent, N.sub.2 is first removed from the crude Ar followed by the removal of O.sub.2 to provide a pure Ar stream. The N.sub.2 -selective adsorbent and O.sub.2 -selective adsorbent are used in different columns. For a given throughput of the feed gas, a lesser number of O.sub.2 -adsorbing columns than N.sub.2 -absorbing columns are used.
The processes described in all of the above patents use multibeds, a large number of valves and vacuum pumps, are cyclic in nature, and are complex to operate. There is a need for an alternate non-cyclic and simple process to remove substantial quantities of O.sub.2 from a crude Ar stream requiring little or no H.sub.2.